A commonly encountered problem with protease-containing liquid detergents is the degradation of second enzymes in the composition by the proteolytic enzyme. The stability of the second enzyme upon storage in product and its effect on cleaning are impaired by the proteolytic enzyme.
Boric acid and boronic acids are known to reversibly inhibit proteolytic enzymes. A discussion of the inhibition of one serine protease, subtilisin, by boronic acid is provided in Philipp, M. and Bender, M. L., "Kinetics of Subtilisin and Thiosubtilisin", Molecular & Cellular Biochemistry, vol. 51, pp. 5-32 (1983).
One type of boronic acid, peptide boronic acid, is discussed as an inhibitor of trypsin-like serine proteases, especially in pharmaceuticals, in European Patent Application 0 293 881, Kettner et al., published Dec. 7, 1988.
German Patent 3 918 761, published Jun. 28, 1990 discloses liquid enzyme concentrate which is said to be usable as a raw material solution for making liquid detergents and the like. The concentrate contains hydrolase, propylene glycol and boric acid or its salt.
U.S. Pat. No. 4,537,707, issued Aug. 27, 1985 describes heavy duty liquid detergents containing artionic surfactants, fatty acid, builder, proteolytic enzyme, boric acid, calcium ions and sodium formate. The combination of boric acid and sodium formate is claimed to provide improved proteolytic enzyme stability in this composition, especially in the presence of a polyol. These compositions are free of lipase.
European Patent Application 0 080 223, published Jun. 1, 1983 describes detergent compositions containing a polyfunctional amino compound or a polyol together with a reducing alkali metal salt.
Similarly in GB 2 079 305, published Jan. 20, 1982, it is disclosed that enhanced enzyme stability can be obtained in a built liquid detergent by inclusion of boric acid, a polyol in the ratio of polyol to boric acid more than 1:1, and a cross-linked polyacrylate polymer. These compositions contain no lipase.
In European Application 0 381 262, Aronson et el., published Aug. 8, 1990, mixtures of proteolytic and lipolytic enzymes in a liquid medium have been disclosed. The stability of lipase is claimed to be improved by the addition of boron compound and a polyol having vicinal hydroxyl groups.
It has now been found that certain aromatic borate esters are especially effective in reversibly inhibiting protease, in a HDL which also comprises detergency ingredients and a second enzyme.
Upon dilution, such as under typical wash conditions, the proteolytic enzyme is no longer inhibited and can function (e.g. to remove protease-sensitive stains from fabrics in the wash).